A technical history of the codebreaking achievements of the U.S Coast Guard Cryptanalytic Unit (a.k.a. Unit #387) during World War II. The unit was founded in 1931 by Elizebeth Smith Friedman, Cryptanalyst-in-Charge, who recruited and trained its codebreakers. In 1941 the unit was absorbed by the U.S. Navy and renamed OP-20-GU, and later OP-G-70, under the command of Lt. Leonard T. Jones, with Elizebeth Friedman as ranking civilian. Starting in 1940, the unit assumed responsibility for monitoring the clandestine radio communications of Nazi spies throughout the Western Hemisphere, and the unit's decrypts of Nazi messages were circulated to the Army, Navy, FBI, and British intelligence. This document describes how the unit broke the codes on dozens of Nazi radio circuits, including circuits that were protected by Kryha and Enigma-model cipher machines.
NARA location: Record Group 38, Crane Material, Inactive Stations, box 57, 5750/2.